PIC16F688 Datasheet, PDF (69/174 Pages) Microchip Technology – 14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

8.1.7 CONFIGURING THE A/D
After the A/D module has been configured as desired,
the selected channel must be acquired before the
conversion is started. The analog input channels must
have their corresponding TRIS bits selected as inputs.
To determine sample time, see Section 14.0 “Electrical
Specifications”. After this sample time has elapsed, the
A/D conversion can be started.
These steps should be followed for an A/D conversion:
1. Configure the A/D module:
• Configure analog/digital I/O (ANSEL)
• Configure voltage reference (ADCON0)
• Select A/D input channel (ADCON0)
• Select A/D conversion clock (ADCON1)
• Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if desired):
• Clear ADIF bit (PIR1<6>)
• Set ADIE bit (PIE1<6>)
• Set PEIE and GIE bits (INTCON<7:6>)
3. Wait the required acquisition time.
4. Start conversion:
• Set GO/DONE bit (ADCON0<0>)
5. Wait for A/D conversion to complete, by either:
• Polling for the GO/DONE bit to be cleared
(with interrupts disabled); OR
• Waiting for the A/D interrupt
6. Read A/D Result register pair
(ADRESH:ADRESL), clear bit ADIF if required.
7. For next conversion, go to step 1 or step 2 as
required. The A/D conversion time per bit is
defined as TAD. A minimum wait of 2 TAD is
required before the next acquisition starts.
PIC16F688
EXAMPLE 8-1: A/D CONVERSION
;This code block configures the A/D
;for polling, Vdd reference, R/C clock
;and RA0 input.
;
;Conversion start & wait for complete
;polling code included.
;
BSF STATUS,RP0 ;Bank 1
MOVLW B’01110000’ ;A/D RC clock
MOVWF ADCON1
BSF TRISA,0
;Set RA0 to input
BSF ANSEL,0
;Set RA0 to analog
BCF STATUS,RP0 ;Bank 0
MOVLW B’10000001’ ;Right, Vdd Vref, AN0
MOVWF ADCON0
CALL SampleTime ;Wait min sample time
BSF ADCON0,GO
;Start conversion
BTFSC ADCON0,GO
;Is conversion done?
GOTO $-1
;No, test again
MOVF ADRESH,W
;Read upper 2 bits
MOVWF RESULTHI
BSF STATUS,RP0 ;Bank 1
MOVF ADRESL,W
;Read lower 8 bits
MOVWF RESULTLO
 2004 Microchip Technology Inc.
Preliminary
DS41203B-page 67